package com.wc.blue_bridge_test.base.T2;

import java.util.Scanner;

/**
 * @Author congege
 * @Description
 * @Date Created in 2023/12/24-12:44
 */
public class Main {
    public static void main(String[] args) {
        Scanner sc = new Scanner(System.in);
        long n = sc.nextInt();
        System.out.println(n * (n + 1) / 2);
    }
}
